Correction of transmission errors



Pace/'ver- Dec. 2, 1947. G. M. GIANNINI 2,432,003

CORRECTION OF TRANSMISSION ERRORS Filed May l5, 1945 2 Sheets-Sheet 1 ffm/ew for' #gat DCC 2, 1947. G. M. GIANNINI CORRECTION OF TRANSMISSION ERRORS 2 sheets-sheet 2 I Filed May 15, 1945 Patented Dec. 2, `1947 2,432,003 CORRECTION OF TRANSMISSION ERRORS Gabriel M. Giannini, West Los Angeles, Calif., as-

signor, by mesne assignments, to Howe & Fant, Inc., South Norwalk, Conn., a. corporation of Delaware Application May 15, 1945, Serial No. 593,953

Claims.

1 The general purpose of the present invention is the correction of errors, inequalities or asynchronisms in a transmission system of any type wherein a rotary or other movable element is driven by an effective applied torque or force in such a manner that the torque forces, and/or the response of the driven member to the torque, are not synchronous with, or do not bear the desired relation to, the initial driving member. The correction system has no applicability to a transmission wherein the -driver and driven members are positively coupled, only having application to transmissions where the over-all coupling (considered as between the initial driving member and the final driven member) is nonpositive and allows or causes deviations from synchronism or from the ideal relationship which may be desired as between the driver and driven members.

The invention is not limited to particular application to any particular transmission system; but the application of the invention to remote control systems of the Selsyn type in which the movements are rotative is typical and illustrative of the invention itself. Accordingly I give the following detailed explanation of the invention as applied to such a transmission system, but without necessary limitation thereto. As applied to such a system, where the ideal angular relationship between transmitter and receiver is an accurately synchronous relation, my correction system modifies the movement of the receiver to correct the inherent torque errors of the Selsyn system to achieve the ideal angular relationship. In the accompanying drawings Fig. 1 is a diagram cf the electrical circuiting of a typical Selsyn system.

Fig. 2 is a plot showing errors inherent in such a system, and their correction by my system;

Fig. 3 is a longitudinal section of a typical receiver for use in a remote control compass system, equipped with the correction devices of my invention;

Fig. 4 is a fragmentary enlarged elevation taken as indicated by line 4--4 on Fig. 3 and showing the correction devices;

Fig. 5 is a similar elevation showing a modified form;

Figs. 6 and 7 are enlarged fragmentary details illustrating the structure shown in Fig. 5, and

Fig. 8 is a diagram illustrative of the action of such a correction device as is shown in Fig. 5.

Fig. 1 shows the essential electrical circuiting of a typical Selsyntransmission system, consisting essentially of a circular resistance unit R to which potential is applied by diametrically opposed brushes B, and which is connected by three-wire circuit C to the delta windings D of a receiver. Theoretic investigation, checked by laboratory tests, has shown that such a system, in addition to errors of a residual nature and errors caused (in a compass system) by deviation, etc., has certain inherent errors of asynchronism which are repetitive in cycles of Considering the angle of rotation of a transmitter counterclockwise from the position marked zero in Fig. l (the angle indicated as 0) the inherent errors in the system through one 60 cycle are plotted in Fig. 2, where the receiver error in degrees is plotted against the transmitter angle, as shown by the plotted curve A. As there shown, the receiver lags the transmitter through the first 30 of transmitter rotation, and then kleads the transmitter through the ensuing 30 of transmitter rotation; the cycle being repeated through each successive 60 of transmitter rotation. The lag and lead of the receiver are symmetric with relation to the 30 position, and maximum receiver error of 1 6 occurs at transmitter anglesv of 13 18 and 46 42 measured from the zero. position or from any succeeding 60 position.

Fig. 3 shows a receiver structure of my design adapted to be used in a Selsyn compass repeater system. As there shown, the receiver coils I0 are rotatably carried by a supporting structure II on a central longitudinal rotatable shaft I2 which carries pointer I3 at its forward end. The coils rotate in the gap between permanent magnets I4 and I5 which are fixed in the case. The electrical connections to the rotating coils -are provided by the collector ring and brush structure shown at I6, the brushes being mounted on the inside of a cap I1 which is secured to and supported on the outer magnet element I5. Central shaft I2 is journalled at its rear end in a bearing I8 in cap I'I; and for the purposes of my present invention the shaft is extended at I2a through the bearing and beyond the rear face of cap Il.

For the correction of the inherent repetitive errors which have been discussed, I provide correction devices such as are shown in Figs. 3' and 4. An annulus 2l) of any suitable material, either non-magnetic or para-magnetic, such as soft iron, is mounted on a hub boss 2| projecting from the rear face of cap I1, so that the annulus is concentric with shaft extension I2a. The annulus may either be mounted in a predetermined xed position, or may be rotatively adjustable about the axis of the shaft.

On the shaft extension, by means of a mounting hub 22 or similar device, I mount a small radially extending magnet 23, preferably a permanent magnet. One polar end of magnet 23 lies inside annulus 20 with a radial clearance such as proportionately indicated in Figs. 3 and 4. Both the magnet 23 and the correction elements 25 are of restricted dimensions in a circumferential direction (thickness) so as to .concentrate their magpetit iields. l

Mounted in and projecting through the annulus are .six magnetic correction elements, ,preferably radially adjustable, and preferably in the form of adjustable screws with axes radial of the shaft and spaced 60 apart around the shaft and annulus. These correction screws are of magnetic material, either individually magnetized or merely of magnetic permeable material. The latter is preferred, with the screws of soft 'iron or steel. If the screws are merely of `magnetic permeable material or if they are magnetized to present at their inner ends polarities opposite `to the polarity presented by magnet 23, or1if 'member 23 be merely magnetically permeable and the .screws magnetized, then there is an attractive action between member 23 and the screws. The immediately following explanation `of the .cor-

rective action of my system will .be based upon the assumption of such an attractive action; the utilization of repulsive action will be spoken of later.

Assuming the action `to be attractive, and assuming for instance that Fig. -4 shows a position of magnet 23 when the transmitter -and receiver are in positions corresponding either to the zero -position indicated in Fig. 1 or any position removed therefrom by 60 or a multiple of 60, the lrelative positions of the correction screws will be asfshownin Fig. 4, that is, at positions of 30, 90, etc. Thus, assuming that Fig. 4 shows magnet 23 standing .in the zero position, then in that po- :sition one correction screw v25a will be located from that zero position in a counter-clockwise direction, and .another correction screw 25h will be located in a position 30 removed clockwise from that zero-position. And a 60 angle of counter-clockwise rotation, corresponding to the 60 .angle of the diagram of Fig. .2, is indicated in Fig. 4.

It will be immediately apparent from consideration of Fig. -4, that, Ywithmagnet 23 standing in zero position or in any of lits successive -60 positions, the magnetic torque forces on magnet VA23 are balanced, and the net .corrective torque cn the. magnet is zero. Also, whenthemagnet vstands in any position directly opposite one .of the-correction screws, themagn-etic corrective `torque for-ce is zero. Between these successive positions in which the magnetic torque force is zero, thatforce varies betweenzero .and a maximum.

For example, consider the action as .magnet 23 rotatesin a counter-clockwise .direction from .the :zero position shownin Fig. 4. As the magnet approaches correction screw 25a, the -attractive Vforce between the magnet and that screw .in-

creases,fwhile the attractive force between the magnet and screw 25h decreases. lAs the magnet approaches screw 25a the magnetic attraction of that screw becomes predominant .and increases .until the magnet reaches .a 'position .at a .determinable .angle from the screw, and then .de-

creases as themagnet further approaches screw 25a, becoming zero again as the magnet lines up A.radially with that screw. Thus, there is a maxi- .mumof counter-clockwise torque applied to mag- V.ne.t..23 at some pointin its vapproach .tofscrew 25a. iollowed by.aA zero torqueas .the magnet reaches v.the .30 .position .opposite .screw .25ct. Then .on 'further .counter-clockwise .movement awayfrom screw 25a.and toward screw 25o there is asimilar attractive action between the magnet and screw 25a,'with a maximum of magnetic Ytorque occurring lwhen thermagnet has Vreached a position at that same determinable angle 'pat the screw, but now exerting a torque in a clockwise direction. And then when the magnet vreaches the 60 position, halfway between screw '25a and screw 25o, the net curve torque on mag- :rotation of magnet 23. And, as will be seen without repetition, the vcycle is repeated for each successive 60 of rotation of magnet 23. Thus, during the first 30 `of rotation of the receiver, from zero position or from any succeeding 60 position, when the receiverferror is negative (lagging) the correction .device .applies aiorwardly .rotating ,correcting torque to the .receiver .to correct that error. And in the ensuing 30 of receiver rotation, where the receiver error is positive (running ahead) ,the correction .deviceapplies a negative vor rearwardly 4rotating torque to .the receiver to correct that error. At rvthe zero position, and at each .successive .30 .position wherethe receiver .error is zero, the magnetic ycorrective torque is also zero.

It may .be .observed that the .simple .correction devices .shown in Fig. 4 will not exactly ,correct the whole .of the inherent .error shown inFg. .2, but the inherent error may .be very -substantially re1duced,.or vreduced to a comparatively negligible quantity, by proper choice of. the constants ,and variables involved in the correction :.device. vA .complete analysis .of all of the magnetic torque forces acting on magnet 23 shows that the'shape of the curve .of the net ycorrection torque, .plotted .against .angular movement, .depends .on the ratio of the radial length of .magnet .2.3 (the radius ,of its outer polar end from the center of shaft I.2a) Ato the radial. distance `of the inner yends .of the correction .elements (screws 25) from the center. .If we call the iirst dimensioni; Vand the second Zz, then the shape .of the correction torque .curve 'and the rotational lengths at which the maximum .Correction torques occur .depend .on the ratio Zi/Zz. .For instance in.Fig. `2 wherea typical .screw 4and q2 .the .charge on :the .magnet end.

Thus,`for the correction of such an error as shown in curve A vof Fig. 2, the bestpracticable shape for the correction torque curve B can be `determined by properly .xingthe ratio l1/l2, and then the best practicable .maxima canbe determined hy choosing proper magnetic charges for the elements 23 and 25. .For instance, a ratio of gives a magnetic torque correction curve ofsuc'h a shape as shownatBin Fig. 2, with maxima b occurring atabout 10 and50".

With the -shape'of curve B-'and the,.maxirna positions thus fixed, 4the amplit-udesfof the maxima are iixediby proper choice of thel quantity qiqz. The choice Aof that vquantity will of course depend on lthe magnitude ofthe restoring polar ends of about 1%-1/8 diameter.

, the quantity qiqz to give such relative maxima as is indicated in Fig. 2, is found to be about 3 (E. M. U.)2. And that quantity can be supy plied, for instance, by utilizing a magnet 23 mag netized to a charge of about 30 E. M. U. and screws 25 of soit iron or steel and having inner With the curve of the correction torque established as shown at B in Fig. 2, the nal net error curve of the receiver is shown by curve C in Fig. 2; the maximum error having been reduced from 1 6 to about or less.

In the instance which is specifically shown in the drawings (magnet 23 is not an element of -the Selsyn system itself) the desired value for the product quantity qiqz may of course be made value of the quantity qiqz will then be attained Iby the proper choice of the quantity q1.

The foregoing illustrative iigures of correction have been given on the basis of the assumption that ring 2) is or non-magnetic material, so that the correction screws 25 are spacedly isolated, so to speak. The action is generally the same as above described if ring 2i) is of magnetic permeable material, except that in such an ar-v rangement the magnetic corrective action of the several screws becomes zero if the screws are withdrawn to a position flush with the inner surface of the ring, and that, to reach any given chosen maxima of corrective torque, the charge quantity qlqz is larger.

The foregoing description of operation has f also been based upon the assumption that the action between members 23 and 25 is attractive. If those several members be so polarized that the spaced correction elements 25 present inner poles of polarities the same as that presented by magnet 23, so that the action becomes repulsive, the only change which need to be made in the correction system is that correction elements 25 should then be placed at the zero position and at the successive 60 positions, instead of at the positions of 90, etc., as shown in Fig. 4.

It may also be observed that the several ad justable correction screws such as shown in Fig. 4 are, when once adjusted for a correction of any given instrument, the full equivalent of predetermined Xed magnetic projections or irregularities in an annulus of para-magnetic material; or are predetermined Xed localized and spaced bodies of magnetic material, if the annulus 20 be considered to be of non-magnetic material.

It can readily be understood without detailed demonstration that if an innite number of correction elements 25 were to be placed in ininitesimal spacing about the annulus, then, by

i ected.

proper radial placements or adjustments of the elements a correction force curve to quite exactly correct any error curve, can be effected. By using a fairly large number` or" the correction elements, that ideal may be approached suiiiciently closely for all practical purposes; and in Figs. 5, 6 and 7 I show correction devices embodying a large number of correction elements and also embodying other modications in design.

In Fig. 5 an annulus 20d is illustrated, concentrically surrounding a rotatable magnetic element 23d, which in this illustration projects radially in opposite directions from shaft 12d. I may here remark that the magnet 23 of Fig. 4 may likewise be double, and that of Fig. 5 may be single. Annulus Zd may be either of magnetic or non-magnetic material, and it may be an annulus which is especially provided for cor rection purposes or it may be an annulus which exists for other functions in the instrument which is to be corrected. And magnetic element 23d may represent any magnetic element either in the instrument or especially provided. These same observations apply to Fig. 4.

In the modiications shown in Fig. 5, instead of radially adjustable screws, I show a plurality of closely spaced partial cylindric insets 25d of magnetic permeable material, set in partial cylindric recesses 25e in the inner face of the annulus. As shown in Figs. 6 and 7, the inserted elements may be rotated between the two extreme positions illustrated, land set either in those positions or in any intermediate position. In various positions, the centers of mass, or what may be regarded as the magnetic centers of the elements, are adjusted to different radial positions with respect to center 12d and with respect to magnetic element 23d. And by proper adjustment the correction torques exerted by each of the elements may be adjusted to any value within the maximum torque range for which the correction device is designed; and a correction curve of substantially any character may be ei- In this manner residual `errors and other errors which are peculiar to an individual instrument and which are non-repetitive in nature may be corrected. And it may be observed that the adaptability of my correction system to errors which are individual and peculiar to an individual instrument or device, is one orf the characteristic advantages of my system of correction. In Selsyn systems, for instance, it has been proposed to introduce corrections in the electrical circuiting of a transmitter; and while it is theoretically possible to correct receiver errors in that manner, no standardized correction system of that type can correct minor or individual errors which are peculiar to the receiver itself; which my system of correction can accomplish.

Fig. 8 is a diagram representing graphically some of the correction effects which may be had with a device embodying adjustable magnetic elements, such for instance as those shown in Fig. 5. Fig. 8 shows several inserts 25e in typical positions in a magnetic body 20e; and directly under each insert the full line curve represents the deviation from average of the magnetic torque exerted by the several inserts on a passing magnetic charge; and the dotted line curve represents the resulting correction torques which are exerted.

Without detailed description, it will be readily understood that the physical arrangement of my `7 correction devices may be reversed. I Vhave described .a device composed vof two relatively rotatable units-the element 23 or Zd and the circular arrangement of correction elements 25 or 25d; with the unit 23 mounted on the shaft to rotate. The same functions will be performed if unit y.'23 is relatively stationary and the unit comprising elements 25 rotates in connection with the shaft. And also, my correction system may be applied to movements other than rotational. In fact it may be applied to correct errors, or to introduce modications of the movements of any member or instrument, cyclically or otherwise, where that member or instrument is not driven positively.

I claim:

l. In a receiver for use in a transmission system, the combination of means for maintaining a magnetic circuit having an air gap, a coil mounted for rotation within the air gap and adapted to move to different positions as current is supplied thereto, and means for correcting the p0- sition of the coil as current is supplied to it, including a pair of magnetic charge carrying units, one being connected to the coil to rotate with it and the other being stationary and disposed about the path of travel of the rotatable unit in magnetically effective relation thereto,

2. In a receiver for use in a transmission system, the combination of means for maintaining a magnetic circuit having an air gap, a shaft mounted for rotation, a coil fast on the shaft and lying within the air gap, the coil and shaft being .adapted-to rotate to different positions as current is supplied to the coil, and means for correcting the position of the coil and shaft as current is supplied to the coil, including a pair of magneticfcharge carrying units, one being stationary and the other connected with the shaft to Yrotate with it in magnetically effective relation to the stationary unit.

3. In a receiver for use in a transmission system, the combination of means for maintaining a magnetic circuit having an air gap, a shaft mounted for rotation, a coil fast on the shaft and lying within the air gap, the coil and shaft being adapted to rotate to different positions as current is supplied to the coil, and means for correcting the jposition .of the `coil andshat `Vas current is supplied to the coil, .including amagnetic member fast on the shaft outside the Aair gap and a plurality of magnetic elements disposed in a circular series along the path lof travel of the member and adjustable to vary their effect on the member.

4. In a receiver for use in a transmission system, the combination of means .for maintaining a magnetic circuit having `an air gap, awshait mounted for rotation, a coi1fast on the. shaft and lying within the air gap, the ycoilarid shaft being adapted to rotate to diierent positionsfas current is supplied to the coil,.andrmeans Yfor correcting the .position ofthe `coil andshaft las current is supplied to the coil, including 1a, magnetic member fast on the shaft,.a; ring encircling the membenand a pluralityo magnetic elements mounted in angularly vspaced relation aboutthe ring and adjustable to vary their effect on the member.

5. In a receiver for use in aptransmissionisystem, the combination of means for maintaining a magnetic circuit having an .air gap, va shaft mounted .for rotation, a coil fast on the shaft and lying within the airggap, the coil and shaft being adapted to rotate vto different v`positionsas current is supplied to the coil, :and means for correcting the position of the coilland shafftfas current is supplied to the coil, including afmagnet fast on the shaft andfextending.outwardly .thereirom, and a plurality .of magnetic elements Vdisposed in a circular series about the path dened by the outer end -of the magnetas it rotates with the shaft, the elements being adjustable with relation to said path to vary their effect on the magnet.

GABRIEL'M. GIANNINI.

REFERENCES CITED The following references are vof record `in the le of this patent:

UNITED STATES PATENTS Number Name Date 217,014 Longfellow July 1, 1879 Ll57,161 Knudsen et al Augl,` .1891 

